A simulation study of structural and optical properties in Cu ions implantation single-crystal rutile
A simulation study of structural and optical properties in Cu ions implantation single-crystal rutile
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DOI：
10.7498/aps.65.206102
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发表时间：
2016-10-20
影响因子：
1
通讯作者：
Wang Cang-Long
中科院分区：
文献类型：
--
作者：
Liu Huan;Li Gong-Ping;Wang Cang-Long
二氧化钛是一种用途广泛的功能材料，用于制造太阳能电池、光水解制氢和光学涂层。从技术上讲，TiO2的吸收边缘位于紫外线区，限制了其应用。铜掺杂可以解决这一关键问题，将吸收边缘从紫外区扩展到可见光区。采用基于密度泛函理论和广义梯度近似和超软赝势的第一性原理计算方法，构建了允许所有原子弛豫的2x2x2超胞，研究了缺陷金红石型TiO2。选取布里渊区k点的2x2x3，平面波截止能量为340 eV。考虑了O空位、Ti空位、Cu间隙、Cu取代Ti和复合缺陷。结构弛豫后，晶格主体发生轻微畸变，晶格参数变化不大，但不影响金红石的晶相。结果表明：价带以o2p态为主，导带以Ti 3d态为主；Cu的空位缺陷由于Cu的三维态而在能隙中产生两个新的杂质能级，Cu取代Ti的空位缺陷由于Cu的三维态与o2p的非键轨道相互作用而在价带附近产生两个新的杂质能级。Ti空位导致费米能级能量降低，在价带顶端产生新的杂质能级，使能隙缩小。O空位能增强费米能级，在导带底部产生一个新的能级，表现出n型半导体性质。Cu取代Ti的浓度越高，带隙越大。这是由于Ti 3d和Cu 3d之间的强相互作用，使得导带向更高的能量移动。不同的复合缺陷有不同的影响。Cu空位和O或Ti空位在带隙内产生新的杂质能级，从而使带隙缩小。同时，间隙铜和空位也可以相互作用。Cu 3d与o2p非键轨道的杂化会在具有Ti空位结构的金红石中产生新的能级，而Cu 3d的非键轨道在具有O空位和Cu间隙的金红石中自行产生新的能级。对含复合缺陷金红石的能带结构进行了分析，结果表明，含O空位和Cu间隙的金红石在可见光范围内有效地影响了吸收边。Cu隙、Cu取代Ti、O空位、Ti空位和化合物缺陷都能使带隙变窄，在可见光谱范围内产生新的吸收峰。结果表明，有缺陷的金红石在可见光范围内提高了吸收，达到了扩大单晶金红石吸收范围的目的。
TiO2 is a versatile functional material in consumer products, such as fabrication of solar cells, light hydrolysis of hydrogen production and optical coating. Technologically, the absorption edge of TiO2 is in the ultraviolet (UV) region, which restrics its applications. Cu doping can solve the crucial problem and extend the absorption edge from the UV to the visible region. The first-principle calculation based on density functional theory with generalized gradient approximation and ultra-soft pseudo-potentials is carried out to investigate the defective rutile TiO2 through using the constructed 2x2x2 supercells in which all atoms are allowed to relax. The plane-wave cutoff energy is 340 eV by selecting 2x2x3 of k-point in Brillouin zone. O vacancy, Ti vacancy, Cu interstitial, Cu substitutional for Ti and compound defects are all considered. After the structural relaxation, the lattice host is slightly distorted with a little change of the lattice parameters, with out affecting the crystalline phase of rutile. The results show that the valence bands are mostly O 2p states while the conduction bands have mainly Ti 3d properties. The defect of Cu interstitial can bring about two new impurity levels in the energy gap because of Cu 3d states, and the defect of Cu substituted for Ti can also induce two new impurity levels while they are next to the valence band due to the interaction between Cu 3d and nonbonding orbits of O 2p. Ti vacancy can cause the Fermi level energy to lower and produce a new impurity level at the top of the valence band, which will narrow the energy gap. O vacancy can enhance the Fermi level energy and produce a new level at the bottom of the conduction bands, which shows the n-type semiconductor properties. The higher the concentration of Cu substituted for Ti, the larger the band gap is. It is due to the strong interaction between Ti 3d and Cu 3d, which makes the conduction band move to higher energy. Different compound defects have different influences. Cu interstitial and O or Ti vacancies induce new impurity levels within the band gap, which narrows the gap. Meanwhile, interstitial Cu and vacancies can also interact with each other. The hybridization between Cu 3d and nonbonding orbits of O 2p will induce new levels in the rutile with Ti vacancy structure, while nonbonding orbits of Cu 3d develop new levels by itself in the rutile with O vacancy and Cu interstitial. The Analysis the band structure of rutile with compound defects, shows that the rutile with O vacancy and Cu interstitial effectively affects influenced the absorption edge in visible light range. Cu interstitial, Cu substituted for Ti, O vacancy, Ti vacancy and compound defects can all narrow the band gap and produce a new absorption peak in the visible spectral range. It indicates that rutile with defects will improve the absorption in the visible range and achieve the goal of expanding the absorption range of single-crystal rutile.